Method and Apparatus for Handling Radio Link Failure

ABSTRACT

A method for handling radio link failure in a user equipment of a wireless communication system is disclosed. The wireless communication system supports Carrier Aggregation such that the UE is able to perform transmission and/or reception through multiple carriers. The method includes steps of configuring a plurality of carriers and controlling a timer utilized for detecting the radio link failure according to a status of a primary carrier within the plurality of carriers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/180,929, filed on May 26, 2009 and entitled “Method and apparatus for improving timing synchronization and Carrier Aggregation in a wireless communication system”, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for handling radio link failure, and more particularly, to a method and apparatus for handling radio link failure in a user equipment of a wireless communication system, so as to reduce waste of radio resources, and enhance the system performance.

2. Description of the Prior Art

Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in base stations (Node Bs) alone rather than in Node Bs and RNC (Radio Network Controller) respectively, so that the system structure becomes simple.

In LTE system, to keep an effective connection between a user equipment (UE) and a Node B after the connection is established, the UE triggers a timer T310 if the UE detects a radio problem, e.g. the UE detects consecutive “out-of-sync” indications from a physical layer (PHY). If the radio problem is not recovered before the timer T310 is expired, the UE determines a radio link failure (RLF) occurs, and triggers a connection re-establishment procedure, to re-establish a normal connection.

Therefore, via the RLF detection, the UE can timely trigger the connection re-establishment procedure, to keep the normal connection with the Node B. However, to meet future requirements of all kinds of communication services, the 3rd Generation Partnership Project (3GPP) has started to work out a next generation of the LTE system: the LTE Advanced (LTE-A) system. Carrier aggregation (CA), where two or more component carriers are aggregated, is introduced into the LTE-A system in order to support wider transmission bandwidths, e.g. up to 100 MHz and for spectrum aggregation. Using CA, the network of the LTE-A system provides multiple component carriers instead of a single carrier for a UE, to establish multiple links for simultaneously receiving and/or transmitting on these component carriers.

At present, the characteristics of CA are quoted as below:

(1) Supporting CA for both contiguous and non-contiguous component carriers.

(2) It is possible to configure a UE to aggregate a different number of component carriers in the uplink (UL) and the downlink (DL), to obtain different bandwidths.

(3) From a UE perspective, there is one transport block and one hybrid-ARQ (HARQ) entity per scheduled component carrier.

As can be seen, a UE with CA configured can utilize multiple component carriers, and each of the component carriers may have a different coverage range or radio quality. Thus, a radio problem on a component carrier does not mean other component carriers are useless, i.e. other component carriers may work. In such a situation, triggering the connection re-establishment procedure seems to be improper and wastes radio resources.

SUMMARY OF THE INVENTION

It is therefore an objective of the present invention to provide a method and apparatus for handling radio link failure in a wireless communication system.

According to the present invention, a method for handling radio link failure in a user equipment (UE) of a wireless communication system is disclosed. The wireless communication system supports Carrier Aggregation such that the UE is able to perform transmission and/or reception through multiple carriers. The method includes steps of configuring a plurality of carriers and controlling a timer utilized for detecting the radio link failure according to a status of a primary carrier within the plurality of carriers.

According to the present invention, a communication device for handling radio link failure in a user equipment of a wireless communication system is disclosed. The wireless communication system supports Carrier Aggregation such that the UE is able to perform transmission and/or reception through multiple carriers. The communication device includes a processor for executing a program, and a memory coupled to the processor for storing the program. The program includes steps of configuring a plurality of carriers, and controlling a timer utilized for detecting the radio link failure according to a status of a primary carrier within the plurality of carriers.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a wireless communications system.

FIG. 2 is a function block diagram of a wireless communications device.

FIG. 3 is a diagram of a program of FIG. 2.

FIG. 4 is a flowchart of a process according to an embodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 1, which illustrates a schematic diagram of a wireless communication system 10. The wireless communication system 10 is preferably an LTE advanced (LTE-A) system, and is briefly composed of a network and a plurality of user equipments (UEs). In FIG. 1, the network and the UEs are simply utilized for illustrating the structure of the wireless communication system 10. Practically, the network may comprise a plurality of base stations (Node Bs), radio network controllers and so on according to actual demands, and the UEs can be devices such as mobile phones, computer systems, etc.

Please refer to FIG. 2, which is a functional block diagram of a communication device 100 in a wireless communication system. The communication device 100 can be utilized for realizing the UEs in FIG. 1. For the sake of brevity, FIG. 2 only shows an input device 102, an output device 104, a control circuit 106, a central processing unit (CPU) 108, a memory 110, a program 112, and a transceiver 114 of the communication device 100. In the communication device 100, the control circuit 106 executes the program 112 in the memory 110 through the CPU 108, thereby controlling an operation of the communication device 100. The communication device 100 can receive signals input by a user through the input device 102, such as a keyboard, and can output images and sounds through the output device 104, such as a monitor or speakers. The transceiver 114 is used to receive and transmit wireless signals, deliver received signals to the control circuit 106, and output signals generated by the control circuit 106 wirelessly. From a perspective of a communication protocol framework, the transceiver 114 can be seen as a portion of Layer 1, and the control circuit 106 can be utilized to realize functions of Layer 2 and Layer 3.

Please continue to refer to FIG. 3. FIG. 3 is a diagram of the program 112 shown in FIG. 2. The program 112 includes an application layer 200, a Layer 3 202, and a Layer 2 206, and is coupled to a Layer 1 218. The Layer 3 performs radio resource control. The Layer 2 comprises a Radio Link Control (RLC) layer and a Medium Access Control (MAC) layer, and performs link control. The Layer 1 218 performs physical connections.

In LTE-A system, the Layer 1 218 and the Layer 2 206 may support a Carrier Aggregation (CA) technology, which enables the UE to perform transmission and/or reception through multiple carriers. In such a situation, the embodiment of the present invention provides a radio link failure (RLF) processing program 220 for appropriately handling RLF, so as to avoid unnecessary connection re-establishment procedures, and thus, enhance the system performance.

Please refer to FIG. 4, which illustrates a schematic diagram of a process 40. The process 40 is utilized for handling RLF in a UE of the wireless communication system 10, and can be compiled into the RLF processing program 220. The process 40 includes the following steps:

Step 400: Start.

Step 402: Configure a plurality of carriers.

Step 404: Control a timer utilized for detecting the radio link failure according to a status of a primary carrier within the plurality of carriers.

Step 406: End.

According to the process 40, after CA is applied, the UE controls the timer used for detecting RLF according to the status of the primary carrier. In other words, other carries, i.e. secondary carriers, do not affect operations of the timer, such that unnecessary connection re-establishment procedures can be avoided, and radio resources can be saved. Noticeably, the aforementioned primary carrier refers to a specific component carrier within all the component carriers after CA is applied, and the denomination of the primary carrier should not make limitation to the present invention. Moreover, the timer for detecting RLF is the aforementioned timer T310. However, the denomination of T310 follows the related radio resource control protocol, and should not make limitation to the present invention.

In short, in the embodiment of the present invention, the timer T310 is affected by the primary carrier and not affected by other carriers. In addition, the timer T310 is not started when timer T300/T301/T304/T311 is running. Therefore, even if a radio problem is detected on a secondary carrier other than the primary carrier, according to the process 40, the Layer 3 202 does not start the timer T310, and thus, the connection re-establishment procedure will not be started. Oppositely, when the Layer 1 218, i.e. PHY layer, indicates a radio problem on the primary carrier, e.g. consecutive out-of-sync situations on the primary carrier are detected, the Layer 3 202 determines that the primary carrier includes a radio problem, and starts the timer T310. If the radio problem is not recovered before the timer T310 is expired, the Layer 3 202 determines occurrence of RLF, and triggers the connection re-establishment procedure, in order to re-establish a normal connection with the network.

As can be seen, the timer T310 for detecting RLF is started in the condition that the primary carrier has a radio problem; thus, unnecessary connection re-establishment procedures can be avoided, so as to save radio resources. In comparison, the prior art does not disclose how to handle RLF after CA is applied.

In summary, when CA is applied, the present invention controls the timer used for detecting RLF according to the status of the primary carrier. As a result, even if secondary carriers have radio problems, the present invention does not trigger the connection re-establishment procedure, so as to prevent waste of radio resources, and enhance the system performance.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

1. A method for handling radio link failure in a user equipment (UE) of a wireless communication system, the wireless communication system supporting Carrier Aggregation (CA) such that the UE is able to perform transmission and/or reception through multiple carriers, the method comprising: configuring a plurality of carriers; and controlling a timer utilized for detecting the radio link failure according to a status of a primary carrier within the plurality of carriers.
 2. The method of claim 1, wherein controlling the timer according to the status of the primary carrier within the plurality of carriers is starting the timer when a radio problem is detected on the primary carrier.
 3. The method of claim 2, wherein the radio problem is detected on the primary carrier when consecutive out-of-sync situations on the primary carrier are detected.
 4. The method of claim 1, further comprising determining the radio link failure occurs on the primary carrier upon expiry of the timer.
 5. The method of claim 1, further comprising triggering a connection re-establishment procedure upon expiry of the timer.
 6. The method of claim 1, wherein the wireless communication system is a Long Term Evolution Advanced (LTE-A) system.
 7. A communication device for handling radio link failure in a user equipment (UE) of a wireless communication system, the wireless communication system supporting Carrier Aggregation (CA) such that the UE is able to perform transmission and/or reception through multiple carriers, the communication device comprising: a processor for executing a program; and a memory coupled to the processor for storing the program; wherein the program comprises: configuring a plurality of carriers; and controlling a timer utilized for detecting the radio link failure according to a status of a primary carrier within the plurality of carriers.
 8. The communication device of claim 7, wherein controlling the timer according to the status of the primary carrier within the plurality of carriers in the program is starting the timer when a radio problem is detected on the primary carrier.
 9. The communication device of claim 8, wherein the radio problem is detected on the primary carrier when consecutive out-of-sync situations on the primary carrier are detected.
 10. The communication device of claim 7, wherein the program further comprises determining the radio link failure occurs on the primary carrier upon expiry of the timer.
 11. The communication device of claim 7, wherein the program further comprises triggering a connection re-establishment procedure upon expiry of the timer.
 12. The communication device of claim 7, wherein the wireless communication system is a Long Term Evolution Advanced (LTE-A) system. 